The goal of this project is to define the molecular mechanisms involved in the replication of enveloped RNA viruses and in particular, to understand the factors which influence the regulation and expression of viral genetic information. Studies are being carried out with the murine leukemia virus system. Current interest is focused on the process of reverse transcription in an effort to corelate genetic structure with enzymatic function. A nonconditional viral mutant which is defective in the pol gene has been shown to produce an abnormally small enzyme with reduced polymerase activity, although its genome size is the same as wild type. Recombinant DNA technology is being used to map the genetic lesion in this mutant. In addition, the defect in enzymatic synthesis of viral DNA is being analyzed in more detail. Another interest concerns the potential use of frog oocytes to study transcription and processing of viral genes. Experiments are in progress to determine whether viral RNA and proteins are expressed following injection of molecularly cloned viral DNA.